Diaphragm cells useful for the electrolysis of brines and the formation of chlorine and caustic soda have an anolyte chamber and a catholyte chamber. The anolyte chamber contains an anolyte solution containing sodium chloride at a pH of from about 2 to about 4.5. Within the anolyte chamber is an anode at which chlorine is evolved. The catholyte chamber contains catholyte liquor at a pH of from about 10 to about 12.5. The catholyte liquor contains sodium hydroxide, and sodium chloride. Sodium hydroxide generated in the catholyte and hydrogen gas is evolved at the cathode.
In the operation of the diaphragm cell, brine containing approximately 300 to 315 grams per liter of sodium chloride is fed into the anolyte .fwdarw.At the anode, the reaction 2Cl.sup.-.fwdarw. Cl.sub.2 +2e.sup.- takes place.
The anolyte liquor passes from the anolyte chamber through the diaphragm into the catholyte chamber and a catholyte product containing from approximately 110 to about 130 grams per liter of sodium hydroxide and from approximately 110 to about 170 grams per liter of sodium chloride is formed. In the catholyte chamber, the reactions Na.sup.+ + OH.sup.- .fwdarw. NaOH, and 2H.sup.+ + 2e.sup.- .fwdarw. H.sub.2 takes place.
Typically, diaphragms for chlorine cells have been constructed of chrysotile asbestos. The chrysotile asbestos provides a diaphragm having a thickness of from about one-eighth of an inch to about one-fourth of an inch. Chrysotile asbestos diaphragms generally have a service life on the order of from about 4 to about 8 months, and most frequently about 6 months.
It is therefore necessary to periodically remove the diaphragm cell from service in order to remove the old diaphragms from the cathodes, and install new diaphragms on the cathodes. This periodic removal of the cell from service results in a consequent loss of production in order to carry out a labor intensive cell renewal operation. In the past, when diaphragm cells used graphite anodes, diaphragm renewal could be coordinated with anode renewal. However, metallic anodes, e.g., coated titanium anodes, have replaced such graphite anodes to a considerable degree. While graphite anodes have a life of from about 4 to about 8 months, the metallic anodes now being used have a life far in excess of 4 to 8 months, e.g., 3 or 4 or more years. Accordingly, the renewal of diaphragms has become a principal factor in cell outage.